Inkjet printers employ printheads in a wide range of applications to form printed documents and, more recently, have found new uses in various types of manufacturing including additive manufacturing systems that are popularly referred to as “3D printers”. Modern inkjet printheads are complex microfluidic devices that often include hundreds or thousands of inkjets, each of which emits drops of ink at precise times in response to firing electrical signals to form high-quality printed images or manufactured articles. The failure of one or more inkjets to eject ink drops during operation of the printhead may negatively impact the quality of printed documents and manufactured articles.
One method that is known to the art that can improve the reliability of inkjet operation in an inkjet printhead is to apply a non-firing electrical signal (also referred to as a “pre-firing” electrical signal) to the inkjets in a short time prior to operating the printhead to eject ink drops. The non-firing electrical signals do not actually eject ink drops from the inkjets, but the inkjets agitate the ink within the microfluidic channels of the printhead in response to the non-firing electrical signals. The agitation produces positive effects in the reliability of the inkjets during subsequent ink drop ejection operations that occur shortly after the inkjets receive the non-firing electrical signals. After long delays without either operation of the inkjet or a purge operation that clears ink from the inkjet, the first few firing cycles from the previously idle inkjet often experience a failure to eject ink drops. In other situations, the inkjet experiences a delay in ejecting the first few ink drops after being idle or the inkjet ejects ink drops with a smaller than normal size. With subsequent firing cycles the drops eventually reach normal velocities and size. The non-firing signals can eliminate the transient deficiencies in drop formation from the idle inkjets.
The application of non-firing signals to inkjets, however, also presents drawbacks that can actually reduce the reliability of the inkjets. For example, if an inkjet receives one or more non-firing signals but does not actually eject drops within a comparatively short time (e.g. within 10-20 seconds), then the non-firing signals may precipitate evaporation and drying of the ink within the inkjet, which produces a clogged inkjet that reduces the reliability of the printhead. In many complex printing operations, a single printhead may use a portion of the inkjets in the printhead to eject ink drops, but a significant portion of the inkjets may remain inactive for a relatively long period only to be required at a later time during a printing operation. Thus, the application of the non-firing electrical signals to the inkjets in a printhead may produce inconsistent results for the printhead since some inkjets may experience improved performance while other inkjets experience degraded performance. Consequently, improvements to inkjet printers that employ non-firing electrical signals to reduce or eliminate these negative effects upon inkjet operation would be beneficial.